EXAMPLE 11 Class limits, class widths, and class boundaries

For the classes in Example 10, find the following:

  1. The lower class limits and the upper class limits
  2. The class width
  3. The class boundaries

Solution

  1. The following table shows the lower class limits and the upper class limits for the classes in Example 10.
    Class Lower class limit
    (smallest value)    		 Upper class limit
    (largest value)
    1–3 1 3
    4–6 4 6
    7–9 7 9

    63

  2. Our lower class limits are 1, 4, and 7; therefore, the class width of each class is 3 because the lower class limits differ by 3. For example, .
  3. To find the class boundary of the first and second class, we find the sum of the upper class limit of the first class and the lower class limit of the second class, and divide this sum by 2, giving us . Similarly, the class boundary of the second class with the third class is . The lower class boundary of the leftmost class equals its upper class boundary minus the class width (that is, ). The upper class boundary of the rightmost class equals its lower class boundary plus the class width (that is, ).